The long-term objective of this research is to identify the origin of neural cell deaths observed in Alzheimer's disease (AD) through investigating molecular details of three types of highly toxic protein assemblies of Alzheimer's -amyloid (A), which are commonly observed in AD. The formation of senile plaques in a brain is a hall mark of Alzheimer's disease (AD); the primary component of the plaque is fibrillar assemblies comprised of A. Because A exhibits toxicity through self-assembly into larger aggregated forms (i.e. monomeric A is non-toxic), it has been long suspected that misfolding of A resulting in the fibril formation and structural changes of A via the self-assembly trigger the onset of the toxicity and the neural dysfunctions in AD. Indeed, the toxicity of the aggregated A is greatly modulated by morphologies of the assembled A, subtle difference in the sequence, and the presence of particular ligands such as Cu(II). In this research, we will examine atomic-level structures of three distinctive forms of toxic amyloid aggregates for A by solid-state NMR (SSNMR), which has been used as a primary tool in structural analysis for amyloid fibrils, including those for A. In Aim 1, we will examine a popular hypothesis that the toxicity of A is associated with Cu(II) binding to A aggregates. It is widely believed that Cu(II)-bound amyloid aggregates may catalyze reactions producing H2O2, which is toxic to neural cells. However, because of the intrinsic heterogeneity of the fibrils, traditional methods in structural biology such as X-ray crystallography and solution NMR are not effective for analysis of the metal-binding structures. With SSNMR, we will examine the location and the mode of Cu(II) binding to A as well as any structural changes due to binding. In Aim 2, we target the structure of amyloid fibrils and diffusible subfibrillar aggregates for A(1-42), which have been poorly characterized, despite their pathogenic importance, because of the extreme difficulties in sample preparation. Molecular structures of these amyloid fibrils and intermediates for A(1-42) have attracted broad attention since the structures offer insights into designs of new therapies and early detection for AD. We will overcome the sample preparation problems by using a novel sensitivity enhancement method, which minimizes sample amount required for SSNMR. The studies will reveal the first site-specific structural details of highly neurotoxic amyloid fibril and intermediate for A(1-42) by SSNMR. In Aim 3, we characterize structure and kinetics in misfolding for E22G A(1-40), which is a unique pathogenic mutant that promotes formation of subfibrillar aggregates. Our study aims to reveal site-specific conformations for E22G A(1-40) fibrils and subfibrillar aggregates for the first time. The neural toxicity of the relevant amyloid aggregates will be examined on mouse PC12 cells.